Hi Jason,
Just got this built. I have added -m32 to the cflags and --32 to AS
flags to get it building on 64bit. You might want to add that.
Just to reiterate the problem. I objdump the usb.bin and I see that
the offset to the string is not relative but absolute.
Here is main
00000110 <main>:
110: 8d 4c 24 04 lea 0x4(%esp),%ecx
114: 83 e4 f0 and $0xfffffff0,%esp
117: ff 71 fc pushl -0x4(%ecx)
11a: 55 push %ebp
11b: 89 e5 mov %esp,%ebp
11d: 51 push %ecx
11e: 83 ec 04 sub $0x4,%esp
121: e8 3c 00 00 00 call 162 <console_init>
126: c7 04 24 45 42 00 00 movl $0x4245,(%esp)
<------ that is the problem line.
12d: e8 ae 00 00 00 call 1e0 <puts>
132: eb fe jmp 132 <main+0x22>
and data; 66, 6f, 6f is 'foo'
00004245 <.rodata.str1.1>:
4245: 66 6f outsw %ds:(%esi),(%dx)
4247: 6f outsl %ds:(%esi),(%dx)
I don't know enough about how this is supposed to work but it looks
like the linker is setting the base to 0x00
.rodata ALIGN(4) :
{
*( .rodata)
} = 0x00
and that is exactly what is in the address, 45 42 00 00.
So, I added -fPIC to the CFLAGS and the code changes to this:
132: 8d 83 cd fa ff ff lea -0x533(%ebx),%eax
138: 89 04 24 mov %eax,(%esp)
13b: e8 b0 00 00 00 call 1f0 <puts>
which seems better since it is building a relative offset but I have
no idea if it is correct.
It seems like there are a few things that need understanding.
1. How to make the code relocatable.
2. Is libpayload being built so that it can be used relocatable.
Marc
--
http://marcjonesconsulting.com